This invention relates in general to injection molding apparatus and in particular to a novel pull core and nozzle arrangement in an injection molding apparatus and a method for operating the same.
In a standard injection molding apparatus which employs a pull core, ordinarily there are separate devices for retracting the nozzle from its injection position and for retracting the pull core from its molding position in the mold cavity. The nozzle is usually attached to an injection carriage which is movable along tie bars. The nozzle may then be moved away from its injection position by moving the entire injection carriage along the tie bars. The injection carriage is usually moved by a hydraulic device. In some instances, the nozzle must be moved in this manner from and to its injection position with each mold cycle. The pull core is also ordinarily moved to and from its molding position with each cycle. Likewise, the pull core is usually moved by a hydraulic device.
Ordinarily, the separate devices for moving the nozzle and the pull core are mounted on different sides of the mold. It is often economical to take advantage of gravitational forces to assist in removing the molded article from the core, and accordingly, the pull core and device moving the pull core may be mounted on the top of the mold, vertically aligned. In this instance, the injection carriage and device moving it are usually mounted on the side of the mold.
Injection molding apparatus designed in the above-described fashion have many disadvantages. The separate devices for moving the injection carriage and pull core are costly. Their relative movement must be timed and controlled by limit switches and other devices which add further cost and may add significantly to the amount of time required for each mold cycle. Additionally, devices commonly used for moving the pull core operate more slowly than the devices commonly used for moving the injection carriage and the time required for each mold cycle is unnecessarily long. Where the nozzle injects through a solid surface of the mold, the channel or runner providing a passage for fluid material from the nozzle to the mold cavity is longer than where the nozzle injects at the parting line between the mold halves. A longer runner adds time to the cycle, wastes material, and adds significantly to the expense of operating the apparatus. Finally, where the injection molding apparatus has the injection carriage mounted on the top for injection at the parting line, the device for retracting the pull core is usually mounted on the side in a manner that often makes changing the mold difficult and time consuming.
It is an object of the invention to provide an injection molding apparatus that is less expensive to manufacture and operate.
Another object of the invention is to provide an injection molding apparatus that requires fewer parts than existing injection molding apparatus.
Another object of the invention is to provide an injection molding apparatus having a reduced mold cycle time.
Another object of the invention is to provide an injection molding apparatus that allows for the easy change of molds.
Still another object of the invention is to provide an injection molding apparatus that may be operated with a reduced number of limit switches.
Still another object of the invention is to provide an injection molding apparatus having a short runner.
Still another object of the invention is to provide injection molding apparatus having an injection carriage and pull core mounted on the same side.
Still another object of the invention is to provide an injection molding apparatus having a single device for advancing and retracting both the nozzle and the pull core.
It is still another object of the invention to provide an injection molding apparatus having a nozzle connected to a pull core in a manner that permits the flow of material from the nozzle and into a runner which connects with the mold cavity.
According to the invention an injection molding apparatus for forming plastic items employs a mold formed of tool members which mate to form a mold cavity. A mold core assembly includes a pull core adapted to extend into the mold cavity and a core support member from which the pull core depends. A nozzle is provided for introducing liquid plastic into a runner which communicates with the mold cavity. The nozzle has a retracted position and an injection position. The nozzle is attached to the mold core assembly such that movement of the nozzle between the retracted position and the injection position causes movement of the pull core, and such that fluid may pass from the nozzle into the runner. The nozzle may be attached to the core support member in a manner to allow the core support member to move laterally with respect to the nozzle.
Also according to the invention in an injection molding apparatus for forming plastic articles employing tool members which mate to form a mold cavity and having a mold core assembly with a pull core adapted to extend into the mold cavity and a nozzle adapted to introduce liquid plastic into the mold cavity, a method for advancing and retracting the pull core is provided. The mold core assembly is attached to the nozzle. The nozzle is advanced in a manner to cause the pull core to move into its molding position. The nozzle may then be retracted in a manner to cause the pull core to move out of its molding position. The mold core assembly may first be aligned with respect to the mold cavity prior to advancing the nozzle, and the mold core assembly may be moved laterally out of alignment with the mold cavity after retracting the nozzle.
Further according to the invention, in an injection molding apparatus for forming plastic articles employing a fixed tool member and a movable tool member which mate to form a mold cavity, having a mold core assembly with a pull core adapted to extend into the mold cavity and a nozzle attached to the mold core assembly, the nozzle adapted to introduce fluid plastic through a runner and into the mold cavity, and the nozzle attached to the mold core assembly in a manner that permits the lateral movement of the mold core assembly with respect to the nozzle, a method for forming a plastic article is provided. The mold cavity is formed and the pull core is aligned with the mold cavity by moving the movable tool member into mating arrangement with the fixed tool member. The nozzle is advanced in a manner to cause the pull core to move into molding position and to cause the nozzle to mate with the runner. Fluid plastic is then injected into the mold cavity where it is allowed to harden. Next the nozzle is retracted in a manner to cause the pull core to withdraw from its molding position. Then the mold cavity is opened by moving the movable tool member laterally with respect to the fixed tool member. The pull core is also moved out of alignment with the mold cavity.